1. Field of the Invention
The present invention relates to a crystal oscillator and more particularly to a circuit substrate on which a crystal vibrator and circuit devices are mounted, and its cover.
2. Description of the Related Art
A crystal oscillator is built in a variety of electronic devices, as the reference source of frequency or time. Such a crystal oscillator includes, for example, a PLL (phase-locked loop) voltage control oscillator usually composed of discrete components.
FIG. 1 is the exploded view of one conventional crystal oscillator.
The crystal oscillator comprises a circuit substrate 13 on which a crystal vibrator 11 composing a voltage control oscillator, and circuit devices 12, such as a voltage variable capacitor device and the like, and its metal cover 14. The circuit substrate 13 is made of glass epoxy and is rectangular with a long side and a short side. The circuit substrate 13 also has grooves 15 formed by through-hole processing at the center of each the long side and each short side. The circuit substrate also has a through-hole connected to a circuit pattern, which is not shown in FIG. 1, in four its corners, and the metal cover 14 is connected to mounting terminals on the base plate.
The metal cover is concave, and has a projection 16 at each aperture end, corresponding to the groove 15 at each long side and each short side of the circuit substrate 13. The metal cover 14 has a swelling from external to internal in the projection 16. The aperture end of the metal cover 14 is mounted around the external circumference of the circuit substrate 13 and is jointed with the circuit substrate 13 by fitting each projection 16 in each groove on each long side and each short side. Then, the metal cover 14 is jointed by soldering with the circuit substrate 13.
In this case, usually, the metal cover 14 on which characters, such as an oscillation frequency, a manufacturer name and the like, are in advance printed is jointed with the circuit substrate 13. Alternatively, after the metal cover 14 is jointed with the circuit substrate 13, characters can be printed on the metal cover 14.
Then, a user sets the crystal oscillator in a set substrate in the reading direction of the characters.
However, any crystal oscillator with such a configuration has a groove 15 at the center of each long side and each short side, and is symmetrical against a center line equally dividing each long or short side into two. Therefore, for example, when the metal cover 14 with printed characters is jointed with the circuit substrate 13, sometimes the reading direction of the characters is inverted, which is a problem.
In this case, if the characters are arrayed from left to right (in the reading direction of characters), as shown in FIG. 2, terminals 21 through 24 are clockwise provided on the rear surface of the circuit substrate 13 in that order. However, if the array of characters is inverted, as shown in FIG. 3, the terminals are clockwise provided in order of the grounding terminal 23, the miscellaneous terminal 24, the power supply terminal 21 and the output terminal 22 when viewed from the reading direction of the characters.
In FIG. 4, the metal cover 14 shown in FIG. 3 is inverted so that the characters can be read.
As shown in FIG. 5, in the set substrate 50 for mounting the crystal oscillator, each circuit terminal is formed in accordance with each terminal of the crystal oscillator. Specifically, a power terminal 51, an output terminal 52, a grounding terminal 53 and a miscellaneous terminal 54 are clockwise formed in accordance with the terminals 21 through 24 of the crystal oscillator whose characters are correctly printed.
Therefore, if the metal cover 14 is jointed with the circuit substrate 13 in such a way that the characters are inverted, each terminal of the crystal oscillator is not matched with each circuit terminal of the set substrate since a user mounts the crystal oscillator on the set substrate 50 in the reading direction of characters. For this reason, even if the crystal oscillator is mounted on the set substrate 50, the crystal oscillator does not correctly operate to incur abnormality.
If the characters are printed on the metal cover 14 after jointing the metal cover 14 with the circuit substrate 13 and assembling the crystal oscillator, sometimes the characters are inverted similarly. In this case too, when mounting the crystal oscillator on the set substrate 50, similarly the crystal oscillator does not correctly operate to incur abnormality.    Patent Reference 1: Japanese Patent Application No. 2000-165177